Conventional tire pressure monitoring systems have battery-powered RF transmitters mounted on a vehicle wheel or tire. The temperature conditions near a vehicle wheel severely affect the battery lifetime of such transmitters. An alternative to the use of battery-powered RF transmitters would be a battery-less transponder mounted in or on the wheel rim or tire. Each transponder would need an associated reader for receiving and processing data received from the transponder. Data could be exchanged between the transponder and the reader using well known transponder techniques such as LF (125 kHz, 134.2 kHz) full or half duplex, HF (13.5 MHz) full duplex or UHF backscatter. However, it would be desirable to have a tire pressure monitoring system that uses fewer components than are presently required.